Because of their excellent moldability, mechanical properties, electrical properties, and so forth, polyolefin resins are used in many different fields as materials for film molding, sheet molding, blow molding, injection molding, and so on.
However, while these resins generally do have excellent properties, they are less than satisfactory in terms of transparency, crystallinity, and rigidity, and in some applications the excellent performance inherent in such resins cannot be fully taken advantage of, and at present this limits the applications of these resins. A technique in which an amide compound is employed has been proposed in the past in an effort to improve the transparency, crystallinity, and rigidity of polyolefin resins (see Patent Documents 1-3).
A number of processes have been disclosed up to now for producing a 1,2,3-propanetricarboxylic acid tris(alkyl-substituted cyclohexylamide) as the above-mentioned amide compound.
For example, Japanese Laid-Open Patent Application H7-242610 (Patent Document 2) gives a preparation example in which 1,2,3-propanetricarboxylic acid tris(cyclohexylamide) and 1,2,3-propanetricarboxylic acid tris(2-methylcyclohexylamide) are obtained by reacting 1,2,3-propanetricarboxylic acid and cyclohexylamine or 2-methylcyclohexylamine in the presence of both triphenyl phosphite and pyridine.
However, the triphenyl phosphite used in this process as an activator of carboxyl groups is extremely expensive, and furthermore, it has to be used in a large quantity, that is, in a stoichiometric amount, and this drives up the cost. Moreover, phosphorous-containing waste liquid is produced, and this necessitates treatment for environmental safety.
In addition, a preparation is given in which 1,2,3-propanetricarboxylic acid trimethyl ester and cyclohexylamine or 2-methylcyclohexylamine used in an amount corresponding to 3 to 30 equivalents thereof are subjected to an ester-amide interchange reaction for 6 hours at 220° C. to obtain a corresponding 1,2,3-propanetricarboxylic acid tris(alkyl-substituted cyclohexylamide) (see Patent Document 4).
However, this process entails a complicated step of producing a methyl ester of 1,2,3-propanetricarboxylic acid, and furthermore the reaction is conducted at a temperature not lower than the boiling point of cyclohexylamine, which means that a costly pressure-resistant equipment is required, and for this and other reasons this process has room for improvement in terms of producing and cost.
Thus, a problem has been that a 1,2,3-propanetricarboxylic acid tris(alkyl-substituted cyclohexylamide) having the specific structure of the present invention cannot always be produced easily and with good productivity with conventional production processes.
Meanwhile, it has been disclosed concerning amidation reaction that in an amidation reaction of N-acylamino acid and a primary amine, secondary amine or ammonia, a boric acid compound effectively serves as a dehydration condensation reaction catalyst, particularly in the presence of an aliphatic alcohol that serves as an auxiliary solvent (see Patent Document 5 and Patent Document 6). Boric acid compounds are inexpensive and readily available. Nevertheless, these publications include neither reference to nor implication of an amidation reaction between a tricarboxylic acid and an alkyl-substituted cyclohexylamine.
Patent Document 1: Japanese Patent No. 3401868
Patent Document 2: Japanese Laid-Open Patent Application H7-242610
Patent Document 3: International Laid-Open Patent Application pamphlet WO/00/52089
Patent Document 4: Japanese Laid-Open Patent Application H7-309821
Patent Document 5: Japanese Laid-Open Patent Application S61-000050
Patent Document 6: Japanese Laid-Open Patent Application 2001-187769